Polyvinyl chloride and polyolefin films are used to provide see-through plastic wraps for meat, produce and other food products. It is important that such films have good anti-static and anti-fogging properties as well as good thermal stability so that the packaged products appear attractive to a consumer.
Anti-static properties relate to the ability of the film to dissipate an electric charge and thereby prevent or control development of static electricity within the film. Films in which static charge has accumulated pick up dust and appear dirty. Accordingly, the appeal of a product packaged in such a film is diminished.
Anti-fogging properties relate to the ability of the film to prevent or dissipate condensation of water vapor in the form of small discrete droplets on the surface of the film. Fog formation causes the contents of a package on which the film is used to appear less visibly attractive and to have reduced food quality.
In addition to good anti-static and anti-fogging properties, a polyvinyl chloride or polyolefin film must also have good dynamic heat stability. Dynamic heat stability relates to the ability of the film to resist color degradation due to heat.
U.S. Pat. No. 3,479,308 issued to Gattenby, Jr., et al. on Nov. 18, 1969 shows a composition for providing anti-fogging and anti-tackifying properties to polymeric vinyl films. The composition includes a glycerol component such as a glycerol monooleate and a polyol component such as polyoxyethylene sorbitan monooleate. The films are said to have excellent anti-tackifying, anti-fogging and gas diffusion properties. However, the necessity for providing good anti-static and heat stability properties as well is not recognized.
U.S. Pat. No. 3,558,537 issued to Hecker et al. on Jan. 26, 1971 discloses a composition including a partial ester of polyglycerol with an unsaturated monocarboxylic acid for improving the anti-fogging properties of a polyvinyl chloride resin. The disadvantage of this patent disclosure is that the importance of providing improved anti-static properties is not taught or suggested.